Your eye has two parts that focus images — the cornea, the clear front surface of your eye, and the lens, a clear structure inside your eye that changes shape to help focus objects. In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature like the surface of a rubber ball. A cornea and lens with such curvature bend (refract) all incoming light the same way, making a sharply focused image on the back of your eye (retina).

However, if your cornea or lens isn't evenly and smoothly curved, light rays aren't refracted properly, and you have a refractive error. Nearsightedness is one type of refractive error. It occurs when your cornea is curved too much or your eye is longer than normal. Instead of being focused precisely on your retina, light is focused in front of your retina, resulting in a blurry appearance for distant objects.

In addition to nearsightedness, other refractive errors include:

• Farsightedness (hyperopia). This occurs when your cornea is curved too little or your eye is shorter than normal. The effect is the opposite of nearsightedness. Light is focused beyond the back of your eye, making nearby objects blurry. You're able to see faraway objects clearly.

• Astigmatism. This occurs when your cornea or lens is curved more steeply in one direction than in another. Uncorrected astigmatism blurs your vision. Typically, the blurred vision occurs more in one direction than in another — horizontally, vertically or diagonally.

If your degree of nearsightedness is pronounced enough that you can't perform a task as well as you wish, or if your quality of vision detracts from your enjoyment of activities, see an eye doctor. He or she can determine the degree of your nearsightedness and advise you of your options to correct your vision.

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